[Python-checkins] r54888 - peps/trunk/pep-3119.txt

Fri Apr 20 20:32:44 CEST 2007

Author: guido.van.rossum
Date: Fri Apr 20 20:32:41 2007
New Revision: 54888

Modified:
   peps/trunk/pep-3119.txt
Log:
Choose Sized instead of Finite.
Make a few more tentative decisions based on Brett's feedback.


Modified: peps/trunk/pep-3119.txt
==============================================================================

--- peps/trunk/pep-3119.txt	(original)
+++ peps/trunk/pep-3119.txt	Fri Apr 20 20:32:41 2007
@@ -240,17 +240,19 @@
     ``StopIteration``.  The concrete ``__iter__`` method returns
     ``self``.  (Note: this assumes PEP 3114 is implemented.)
 
-``Finite``
+``Sized``
     The base class for classes defining ``__len__``.  The ``__len__``
     method should return an ``Integer`` (see "Numbers" below) >= 0.
     The abstract ``__len__`` method returns 0.  **Invariant:** If a
-    class ``C`` derives from ``Finite`` as well as from ``Iterable``,
+    class ``C`` derives from ``Sized`` as well as from ``Iterable``,
     the invariant ``sum(1 for x in o) == len(o)`` should hold for any
-    instance ``o`` of ``C``.  **Open issue:** ``Finite`` may be a
-    confusing name.  Other alternatives already rejected: ``Lengthy``,
-    ``Sizeable`` (both too cute), ``Countable`` (the set of natural
-    numbers is a countable set in math).  We may just have to teach
-    people what we mean...
+    instance ``o`` of ``C``.  **Open issue:** Is ``Sized`` the best
+    name?  Proposed alternatives already tentatively rejected:
+    ``Finite`` (nobody understood it), ``Lengthy``, ``Sizeable`` (both
+    too cute), ``Countable`` (the set of natural numbers is a
+    countable set in math), ``Enumerable`` (sounds like a sysnonym for
+    ``Iterable``), ``Dimension``, ``Extent`` (sound like numbers to
+    me).
 
 ``Container``
     The base class for classes defining ``__contains__``.  The
@@ -301,7 +303,7 @@
 
 ``Set``
     This is a finite, iterable container, i.e. a subclass of
-    ``Finite``, ``Iterable`` and ``Container``.  Not every subset of
+    ``Sized``, ``Iterable`` and ``Container``.  Not every subset of
     those three classes is a set though!  Sets have the additional
     invariant that each element occurs only once (as can be determined
     by iteration), and in addition sets define concrete operators that
@@ -309,7 +311,7 @@
 
     Sets with different implementations can be compared safely,
     efficiently and correctly.  Because ``Set`` derives from
-    ``Finite``, ``__eq__`` takes a shortcut and returns ``False``
+    ``Sized``, ``__eq__`` takes a shortcut and returns ``False``
     immediately if two sets of unequal length are compared.
     Similarly, ``__le__`` returns ``False`` immediately if the first
     set has more members than the second set.  Note that set inclusion
@@ -380,18 +382,20 @@
         Abstract method that empties the set.  (Making this concrete
         would just add a slow, cumbersome default implementation.)
 
-    **Open issues:** Should we support more operations implemented by
-    the Python 2 ``set`` type?  E.g. pop, update, __ior__,
-    intersection_update, __iand__, difference_update, __ixor__,
-    symmetric_difference_update, __isub__.  Should we unify ``remove``
-    and ``discard``, a la Java (which has a single method returning
-    a boolean indicating whether it was removed or not)?
-
-    Note that in Python 2, ``a.update(b)`` is not exactly the same as
-    ``a |= b``, since ``update()`` takes any iterable for an argument,
-    while ``|=`` requires another set; similar for the other
-    operators.  What to do about this?  Do we really want the method
-    explosion that comes from this distinction?
+    ``.pop()``
+        Concrete method that removes an arbitrary item.  If the set is
+        empty, it raises ``KeyError``.  The default implementation
+        removes the first item returned by the set's iterator.
+
+    This also supports the in-place mutating operations ``|=``,
+    ``&=``, ``^=``, ``-=``.  It does not support the named methods
+    that perform (almost) the same operations, like ``update``, even
+    though these don't have exactly the same rules (``update`` takes
+    any iterable, while ``|=`` requires a set).
+
+    **Open issues:** Should we unify ``remove`` and ``discard``, a la
+    Java (which has a single method returning a boolean indicating
+    whether it was removed or not)?
 
 
 Mappings
@@ -426,7 +430,7 @@
     iteration never ends.
 
 ``Mapping``
-    A subclass of ``IterableMapping`` and ``Finite``.  It defines
+    A subclass of ``IterableMapping`` and ``Sized``.  It defines
     concrete methods ``__eq__``, ``keys``, ``items``, ``values``.  The
     lengh of such an object should equal to the number of elements
     returned by iterating over the object until the end of the
@@ -445,18 +449,15 @@
 
 ``MutableMapping``
     A subclass of ``Mapping`` that also implements some standard
-    mutating methods.  At least ``__setitem__``, ``__delitem__``,
-    ``clear``, ``update``.
 
-**Open Issues:**
-
-* What about pop, popitem, setdefault?  (``MutableSequence`` does have
-  ``pop``.  Though it's not quite the same.)
+    mutating methods.  Abstract methods include ``__setitem__``,
+    ``__delitem__``, ``clear``, ``update``.  Concrete methods include
+    ``pop``, ``popitem``.  Note: ``setdefault`` is *not* included.
 
 * Do we need BasicMapping and IterableMapping?  We should probably
   just start with Mapping.
 
-* We should say something about mapping view types, too.
+* We should say more about mapping view types.
 
 
 Sequences
@@ -469,7 +470,7 @@
 from ``HashableSequence``.
 
 ``Sequence``
-    A subclass of ``Iterable``, ``Finite``, ``Container``.  It
+    A subclass of ``Iterable``, ``Sized``, ``Container``.  It
     defines a new abstract method ``__getitem__`` that has a
     complicated signature: when called with an integer, it returns an
     element of the sequence or raises ``IndexError``; when called with
@@ -494,12 +495,10 @@
     Abstract mutating methods: ``__setitem__`` (for integer indices as
     well as slices), ``__delitem__`` (ditto), ``insert``, ``append``,
     ``reverse``.  Concrete mutating methods: ``extend``, ``pop``,
-    ``remove``.  Note: this does not define ``sort()`` -- that is only
-    required to exist on genuine ``list`` instances.
-
-    **Open issues:** What about ``+=`` and ``*=``?  (Including these
-    in the spec would clarify that they are *required* to be
-    implemented as in-place modifications.)
+    ``remove``.  Concrete mutating operators: ``+=``, ``*=`` (these
+    mutate the object in place).  Note: this does not define
+    ``sort()`` -- that is only required to exist on genuine ``list``
+    instances.
 
 
 ABCs for Numbers
